It has been proposed that estrogen delays and or prevents the onset of hypertension and may function to keep women "cardiovascularly younger" than men of the same age. Similar observations have been made in experimental hypertensive animals, however, the underlying mechanisms of estrogen's protective effects are incompletely understood. Given the importance of estrogen replacement therapy in women's health, it is clear that an understanding of the cellular mechanisms underlying estrogen's cardiovascular protective effects is critical for continuing development of clinical therapies for the treatment of hypertension in women. Angiotensin II (Ang II) is an important factor in some forms of both clinical and experimental hypertension. Chronic intravenous infusions of low levels of Ang II in experimental animals result in an increase in blood pressure that involves an increased neurogenic contribution to the maintenance of blood pressure which is prevented by prior lesioning of the area postrema (3,6,33,57,95). It is thought that circulating Ang II acts on area postrema neurons to maintain the hypertension. The proposed studies will test the general hypothesis that estrogen protects against the Ang II induced hypertension by inhibiting the actions of Ang II on area postrema neurons. To test this hypothesis and to characterize the effects of estrogen (17beta-estradiol) on area postrema neurons, Ang II induced increases in blood pressure and baroreflex modulation, this proposal will utilize whole-cell patch clamp recordings from isolated area postrema neurons, in vivo single unit recordings of area postrema neurons and hemodynamic measurements in conscious animals to address the following 4 major and distinct aims. 1) To evaluate area postrema membrane properties following exposure to 17beta-estradiol. 2) To determine the effects of acute and chronic 17beta-estradiol on area postrema calcium handling. 3) To determine the effect of 17beta-estradiol on activation of area postrema neurons. 4) To evaluate the effects of acute and chronic 17beta-estradiol on Ang II hypertension. Determination of the effects of estrogen on CNS mechanisms underlying Ang II dependent hypertension will have a significant impact on our understanding of the cardiovascular benefits of estrogen replacement therapy.